US9158630B1

US9158630B1 - Testing integrity of replicated storage

Info

Publication number: US9158630B1
Application number: US14/133,945
Authority: US
Inventors: Assaf Natanzon
Original assignee: EMC Corp
Current assignee: EMC Corp
Priority date: 2013-12-19
Filing date: 2013-12-19
Publication date: 2015-10-13

Abstract

In one aspect, a method includes marking a list of locations currently being shipped to a replica site, generating course granularity hash signatures of data for each area of memory in the snapshot volume, generating fine granularity hash signatures of data for each subarea of memory in the snapshot volume, sending course granularity hash signatures to the replica site for each area not being changed in a production volume and sending fine granularity hash signatures to the replica site for each area being changed in the production volume. The snapshot volume is a snapshot of the production volume.

Description

BACKGROUND

Computer data is vital to today's organizations and a significant part of protection against disasters is focused on data protection. As solid-state memory has advanced to the point where cost of memory has become a relatively insignificant factor, organizations can afford to operate with systems that store and process terabytes of data.

Conventional data protection systems include tape backup drives, for storing organizational production site data on a periodic basis. Another conventional data protection system uses data replication, by creating a copy of production site data of an organization on a secondary backup storage system, and updating the backup with changes. The backup storage system may be situated in the same physical location as the production storage system, or in a physically remote location. Data replication systems generally operate either at the application level, at the file system level, or at the data block level.

SUMMARY

In another aspect, an apparatus includes electronic hardware circuitry configured to mark a list of locations currently being shipped to a replica site, generate course granularity hash signatures of data for each area of memory in the snapshot volume, generate fine granularity hash signatures of data for each subarea of memory in the snapshot volume, send course granularity hash signatures to the replica site for each area not being changed in a production volume and send fine granularity hash signatures to the replica site for each area being changed in the production volume. The snapshot volume is a snapshot of the production volume.

In a further aspect, an article includes a non-transitory computer-readable medium that stores computer-executable instructions. The instructions cause a machine to mark a list of locations currently being shipped to a replica site, generate course granularity hash signatures of data for each area of memory in the snapshot volume, the snapshot volume being a snapshot of a production volume, generate fine granularity hash signatures of data for each subarea of memory in the snapshot volume, send course granularity hash signatures to the replica site for each area not being changed in the production volume and send fine granularity hash signatures to the replica site for each area being changed in the production volume.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an example of a data protection system used with a continuous replication mode.

FIG. 2 is an illustration of an example of a journal history of write transactions for a storage system.

FIG. 3 is a block diagram of an example of a data protection system used with a snapshot shipping mode.

FIG. 4 is a flowchart of an example of a process to replicate data from a production site to a replication site using the snapshot shipping mode.

FIGS. 5 to 7 are flowcharts of an example of processes used to test the integrity of a replicated storage.

FIGS. 8 and 9 are flowcharts of processes used to focus integrity testing within a replicate storage.

FIG. 10 is a computer on which any of the processes of FIGS. 5 to 9 may be implemented.

DETAILED DESCRIPTION

Described herein are techniques to test the integrity of a replicated storage.

The following definitions may be useful in understanding the specification and claims.

BACKUP SITE—a facility where replicated production site data is stored; the backup site may be located in a remote site or at the same location as the production site;

BOOKMARK—a bookmark is metadata information stored in a replication journal which indicates a point in time.

DATA PROTECTION APPLIANCE (DPA)—a computer or a cluster of computers responsible for data protection services including inter alia data replication of a storage system, and journaling of I/O requests issued by a host computer to the storage system;

HASH SIGNATURE—a hash signature is generated using an algorithm such as a cryptographic hash function (e.g., SHA-1 or SHA-2) and sometimes referred to herein as a signature;

HOST—at least one computer or networks of computers that runs at least one data processing application that issues I/O requests to one or more storage systems; a host is an initiator with a SAN;

HOST DEVICE—an internal interface in a host, to a logical storage unit;

IMAGE—a copy of a logical storage unit at a specific point in time;

INITIATOR—a node in a SAN that issues I/O requests;

I/O DATA—Data that will be or is written to a volume by, for example, an application, sometimes called write transaction data or write data;

I/O REQUEST—an input/output request (sometimes referred to as an I/O), which may be a read I/O request (sometimes referred to as a read request or a read) or a write I/O request (sometimes referred to as a write request or a write);

JOURNAL—a record of write transactions issued to a storage system; used to maintain a duplicate storage system, and to roll back the duplicate storage system to a previous point in time;

LOGICAL UNIT—a logical entity provided by a storage system for accessing data from the storage system. The logical disk may be a physical logical unit or a virtual logical unit;

LUN—a logical unit number for identifying a logical unit;

PHYSICAL LOGICAL UNIT—a physical entity, such as a disk or an array of disks, for storing data in storage locations that can be accessed by address;

PRODUCTION SITE—a facility where one or more host computers run data processing applications that write data to a storage system and read data from the storage system;

REMOTE ACKNOWLEDGEMENTS—an acknowledgement from remote DPA to the local DPA that data arrived at the remote DPA (either to the appliance or the journal);

SIGNATURE—a signature is a hash signature;

SPLITTER ACKNOWLEDGEMENT—an acknowledgement from a DPA to the protection agent (splitter) that data has been received at the DPA; this may be achieved by an SCSI status command;

SAN—a storage area network of nodes that send and receive an I/O and other requests, each node in the network being an initiator or a target, or both an initiator and a target;

SOURCE SIDE—a transmitter of data within a data replication workflow, during normal operation a production site is the source side; and during data recovery a backup site is the source side, sometimes called a primary side;

STORAGE SYSTEM—a SAN entity that provides multiple logical units for access by multiple SAN initiators;

TARGET—a node in a SAN that replies to I/O requests;

TARGET SIDE—a receiver of data within a data replication workflow; during normal operation a back site is the target side, and during data recovery a production site is the target side, sometimes called a secondary side;

VIRTUAL LOGICAL UNIT—a virtual storage entity which is treated as a logical unit by virtual machines;

WAN—a wide area network that connects local networks and enables them to communicate with one another, such as the Internet.

A description of journaling and some techniques associated with journaling may be described in the patent titled “METHODS AND APPARATUS FOR OPTIMAL JOURNALING FOR CONTINUOUS DATA REPLICATION” and with U.S. Pat. No. 7,516,287, which is hereby incorporated by reference.

AN EXAMPLE OF A REPLICATION SYSTEM USED WITH A CONTINUOUS REPLICATION MODE (FIGS. 1 AND 2)

Referring to FIG. 1, a data protection system 100 includes two sites; Site I, which is a production site, and Site II, which is a backup site or replica site. Under normal operation the production site is the source side of system 100, and the backup site is the target side of the system. The backup site is responsible for replicating production site data. Additionally, the backup site enables roll back of Site I data to an earlier pointing time, which may be used in the event of data corruption of a disaster, or alternatively in order to view or to access data from an earlier point in time.

FIG. 1 is an overview of a system for data replication of either physical or virtual logical units. Thus, one of ordinary skill in the art would appreciate that in a virtual environment a hypervisor, in one example, would consume logical units and generate a distributed file system on them such as VMFS creates files in the file system and expose the files as logical units to the virtual machines (each VMDK is seen as a SCSI device by virtual hosts). In another example, the hypervisor consumes a network based file system and exposes files in the NFS as SCSI devices to virtual hosts.

During normal operations, the direction of replicate data flow goes from source side to target side. It is possible, however, for a user to reverse the direction of replicate data flow, in which case Site I starts to behave as a target backup site, and Site II starts to behave as a source production site. Such change of replication direction is referred to as a “failover”. A failover may be performed in the event of a disaster at the production site, or for other reasons. In some data architectures, Site I or Site II behaves as a production site for a portion of stored data, and behaves simultaneously as a backup site for another portion of stored data. In some data architectures, a portion of stored data is replicated to a backup site, and another portion is not.

The production site and the backup site may be remote from one another, or they may both be situated at a common site, local to one another. Local data protection has the advantage of minimizing data lag between target and source, and remote data protection has the advantage is being robust in the event that a disaster occurs at the source side.

The source and target sides communicate via a wide area network (WAN) 128, although other types of networks may be used.

Each side of system 100 includes three major components coupled via a storage area network (SAN); namely, (i) a storage system, (ii) a host computer, and (iii) a data protection appliance (DPA). Specifically with reference to FIG. 1, the source side SAN includes a source host computer 104, a source storage system 108, and a source DPA 112. Similarly, the target side SAN includes a target host computer 116, a target storage system 120, and a target DPA 124. As well, the protection agent (sometimes referred to as a splitter) may run on the host, or on the storage, or in the network or at a hypervisor level, and that DPAs are optional and DPA code may run on the storage array too, or the DPA 124 may run as a virtual machine.

Generally, a SAN includes one or more devices, referred to as “nodes”. A node in a SAN may be an “initiator” or a “target”, or both. An initiator node is a device that is able to initiate requests to one or more other devices; and a target node is a device that is able to reply to requests, such as SCSI commands, sent by an initiator node. A SAN may also include network switches, such as fiber channel switches. The communication links between each host computer and its corresponding storage system may be any appropriate medium suitable for data transfer, such as fiber communication channel links.

The host communicates with its corresponding storage system using small computer system interface (SCSI) commands.

System

100 includes source storage system 108 and target storage system 120. Each storage system includes physical storage units for storing data, such as disks or arrays of disks. Typically,

storage systems

108 and 120 are target nodes. In order to enable initiators to send requests to storage system 108, storage system 108 exposes one or more logical units (LU) to which commands are issued. Thus,

storage systems

108 and 120 are SAN entities that provide multiple logical units for access by multiple SAN initiators.

Logical units are a logical entity provided by a storage system, for accessing data stored in the storage system. The logical unit may be a physical logical unit or a virtual logical unit. A logical unit is identified by a unique logical unit number (LUN). Storage system 108 exposes a logical unit 136, designated as LU A, and storage system 120 exposes a logical unit 156, designated as LU B.

LU B is used for replicating LU A. As such, LU B is generated as a copy of LU A. In one embodiment, LU B is configured so that its size is identical to the size of LU A. Thus, for LU A, storage system 120 serves as a backup for source side storage system 108. Alternatively, as mentioned hereinabove, some logical units of storage system 120 may be used to back up logical units of storage system 108, and other logical units of storage system 120 may be used for other purposes. Moreover, there is symmetric replication whereby some logical units of storage system 108 are used for replicating logical units of storage system 120, and other logical units of storage system 120 are used for replicating other logical units of storage system 108.

System

100 includes a source side host computer 104 and a target side host computer 116. A host computer may be one computer, or a plurality of computers, or a network of distributed computers, each computer may include inter alia a conventional CPU, volatile and non-volatile memory, a data bus, an I/O interface, a display interface and a network interface. Generally a host computer runs at least one data processing application, such as a database application and an e-mail server.

Generally, an operating system of a host computer creates a host device for each logical unit exposed by a storage system in the host computer SAN. A host device is a logical entity in a host computer, through which a host computer may access a logical unit. Host device 104 identifies LU A and generates a corresponding host device 140, designated as Device A, through which it can access LU A. Similarly, host computer 116 identifies LU B and generates a corresponding device 160, designated as Device B.

In the course of continuous operation, host computer 104 is a SAN initiator that issues I/O requests (write/read operations) through host device 140 to LU A using, for example, SCSI commands. Such requests are generally transmitted to LU A with an address that includes a specific device identifier, an offset within the device, and a data size. Offsets are generally aligned to 512 byte blocks. The average size of a write operation issued by host computer 104 may be, for example, 10 kilobytes (KB); i.e., 20 blocks. For an I/O rate of 50 megabytes (MB) per second, this corresponds to approximately 5,000 write transactions per second.

System

100 includes two data protection appliances, a source side DPA 112 and a target side DPA 124. A DPA performs various data protection services, such as data replication of a storage system, and journaling of I/O requests issued by a host computer to source side storage system data. As explained in detail herein, when acting as a target side DPA, a DPA may also enable roll back of data to an earlier point in time, and processing of rolled back data at the target site. Each

DPA

112 and 124 is a computer that includes inter alia one or more conventional CPUs and internal memory.

For additional safety precaution, each DPA is a cluster of such computers. Use of a cluster ensures that if a DPA computer is down, then the DPA functionality switches over to another computer. The DPA computers within a DPA cluster communicate with one another using at least one communication link suitable for data transfer via fiber channel or IP based protocols, or such other transfer protocol. One computer from the DPA cluster serves as the DPA leader. The DPA cluster leader coordinates between the computers in the cluster, and may also perform other tasks that require coordination between the computers, such as load balancing.

In the architecture illustrated in FIG. 1, DPA 112 and DPA 124 are standalone devices integrated within a SAN. Alternatively, each of DPA 112 and DPA 124 may be integrated into storage system 108 and storage system 120, respectively, or integrated into host computer 104 and host computer 116, respectively. Both DPAs communicate with their respective host computers through communication lines such as fiber channels using, for example, SCSI commands or any other protocol.

DPAs

112 and 124 are configured to act as initiators in the SAN; i.e., they can issue I/O requests using, for example, SCSI commands, to access logical units on their respective storage systems. DPA 112 and DPA 124 are also configured with the necessary functionality to act as targets; i.e., to reply to I/O requests, such as SCSI commands, issued by other initiators in the SAN, including inter alia their

respective host computers

104 and 116. Being target nodes, DPA 112 and DPA 124 may dynamically expose or remove one or more logical units.

As described hereinabove, Site I and Site II may each behave simultaneously as a production site and a backup site for different logical units. As such, DPA 112 and DPA 124 may each behave as a source DPA for some logical units, and as a target DPA for other logical units, at the same time.

Host computer

104 and host computer 116 include

protection agents

144 and 164, respectively.

Protection agents

144 and 164 intercept SCSI commands issued by their respective host computers, via host devices to logical units that are accessible to the host computers. A data protection agent may act on an intercepted SCSI commands issued to a logical unit, in one of the following ways: send the SCSI commands to its intended logical unit; redirect the SCSI command to another logical unit; split the SCSI command by sending it first to the respective DPA; after the DPA returns an acknowledgement, send the SCSI command to its intended logical unit; fail a SCSI command by returning an error return code; and delay a SCSI command by not returning an acknowledgement to the respective host computer.

A protection agent may handle different SCSI commands, differently, according to the type of the command. For example, a SCSI command inquiring about the size of a certain logical unit may be sent directly to that logical unit, while a SCSI write command may be split and sent first to a DPA associated with the agent. A protection agent may also change its behavior for handling SCSI commands, for example as a result of an instruction received from the DPA.

Specifically, the behavior of a protection agent for a certain host device generally corresponds to the behavior of its associated DPA with respect to the logical unit of the host device. When a DPA behaves as a source site DPA for a certain logical unit, then during normal course of operation, the associated protection agent splits I/O requests issued by a host computer to the host device corresponding to that logical unit. Similarly, when a DPA behaves as a target device for a certain logical unit, then during normal course of operation, the associated protection agent fails I/O requests issued by host computer to the host device corresponding to that logical unit.

Communication between protection agents and their respective DPAs may use any protocol suitable for data transfer within a SAN, such as fiber channel, or SCSI over fiber channel. The communication may be direct, or via a logical unit exposed by the DPA. Protection agents communicate with their respective DPAs by sending SCSI commands over fiber channel.

Protection agents

144 and 164 are drivers located in their

respective host computers

104 and 116. Alternatively, a protection agent may also be located in a fiber channel switch, or in any other device situated in a data path between a host computer and a storage system or on the storage system itself. In a virtualized environment, the protection agent may run at the hypervisor layer or in a virtual machine providing a virtualization layer.

What follows is a detailed description of system behavior under normal production mode, and under recovery mode.

In production mode DPA 112 acts as a source site DPA for LU A. Thus, protection agent 144 is configured to act as a source side protection agent; i.e., as a splitter for host device A. Specifically, protection agent 144 replicates SCSI I/O write requests. A replicated SCSI I/O write request is sent to DPA 112. After receiving an acknowledgement from DPA 124, protection agent 144 then sends the SCSI I/O write request to LU A. After receiving a second acknowledgement from storage system 108

host computer

104 acknowledges that an I/O command complete.

When DPA 112 receives a replicated SCSI write request from data protection agent 144, DPA 112 transmits certain I/O information characterizing the write request, packaged as a “write transaction”, over WAN 128 to DPA 124 on the target side, for journaling and for incorporation within target storage system 120.

DPA

112 may send its write transactions to DPA 124 using a variety of modes of transmission, including inter alia (i) a synchronous mode, (ii) an asynchronous mode, and (iii) a snapshot mode. In synchronous mode, DPA 112 sends each write transaction to DPA 124, receives back an acknowledgement from DPA 124, and in turns sends an acknowledgement back to protection agent 144. Protection agent 144 waits until receipt of such acknowledgement before sending the SCSI write request to LU A.

In asynchronous mode, DPA 112 sends an acknowledgement to protection agent 144 upon receipt of each I/O request, before receiving an acknowledgement back from DPA 124.

In snapshot mode, DPA 112 receives several I/O requests and combines them into an aggregate “snapshot” of all write activity performed in the multiple I/O requests, and sends the snapshot to DPA 124, for journaling and for incorporation in target storage system 120. In snapshot mode DPA 112 also sends an acknowledgement to protection agent 144 upon receipt of each I/O request, before receiving an acknowledgement back from DPA 124.

For the sake of clarity, the ensuing discussion assumes that information is transmitted at write-by-write granularity.

While in production mode, DPA 124 receives replicated data of LU A from DPA 112, and performs journaling and writing to storage system 120. When applying write operations to storage system 120, DPA 124 acts as an initiator, and sends SCSI commands to LU B.

During a recovery mode, DPA 124 undoes the write transactions in the journal, so as to restore storage system 120 to the state it was at, at an earlier time.

As described hereinabove, LU B is used as a backup of LU A. As such, during normal production mode, while data written to LU A by host computer 104 is replicated from LU A to LU B, host computer 116 should not be sending I/O requests to LU B. To prevent such I/O requests from being sent, protection agent 164 acts as a target site protection agent for host Device B and fails I/O requests sent from host computer 116 to LU B through host Device B.

Target storage system

120 exposes a logical unit 176, referred to as a “journal LU”, for maintaining a history of write transactions made to LU B, referred to as a “journal”. Alternatively, journal LU 176 may be striped over several logical units, or may reside within all of or a portion of another logical unit. DPA 124 includes a journal processor 180 for managing the journal.

Journal processor

180 functions generally to manage the journal entries of LU B. Specifically, journal processor 180 enters write transactions received by DPA 124 from DPA 112 into the journal, by writing them into the journal LU, reads the undo information for the transaction from LU B, updates the journal entries in the journal LU with undo information, applies the journal transactions to LU B, and removes already-applied transactions from the journal.

Referring to FIG. 2, which is an illustration of a write transaction 200 for a journal. The journal may be used to provide an adaptor for access to storage 120 at the state it was in at any specified point in time. Since the journal contains the “undo” information necessary to roll back storage system 120, data that was stored in specific memory locations at the specified point in time may be obtained by undoing write transactions that occurred subsequent to such point in time.

Write transaction

200 generally includes the following fields: one or more identifiers; a time stamp, which is the date & time at which the transaction was received by source side DPA 112; a write size, which is the size of the data block; a location in journal LU 176 where the data is entered; a location in LU B where the data is to be written; and the data itself.

Write transaction

200 is transmitted from source side DPA 112 to target side DPA 124. As shown in FIG. 2, DPA 124 records the write transaction 200 in the journal that includes four streams. A first stream, referred to as a DO stream, includes new data for writing in LU B. A second stream, referred to as an DO METADATA stream, includes metadata for the write transaction, such as an identifier, a date & time, a write size, a beginning address in LU B for writing the new data in, and a pointer to the offset in the DO stream where the corresponding data is located. Similarly, a third stream, referred to as an UNDO stream, includes old data that was overwritten in LU B; and a fourth stream, referred to as an UNDO METADATA, include an identifier, a date & time, a write size, a beginning address in LU B where data was to be overwritten, and a pointer to the offset in the UNDO stream where the corresponding old data is located.

In practice each of the four streams holds a plurality of write transaction data. As write transactions are received dynamically by target DPA 124, they are recorded at the end of the DO stream and the end of the DO METADATA stream, prior to committing the transaction. During transaction application, when the various write transactions are applied to LU B, prior to writing the new DO data into addresses within the storage system, the older data currently located in such addresses is recorded into the UNDO stream. In some examples, the metadata stream (e.g., UNDO METADATA stream or the DO METADATA stream) and the data stream (e.g., UNDO stream or DO stream) may be kept in a single stream each (i.e., one UNDO data and UNDO METADATA stream and one DO data and DO METADATA stream) by interleaving the metadata into the data stream.

AN EXAMPLE OF A REPLICATION SYSTEM USED WITH A SNAPSHOT SHIPPING MODE (FIGS. 3 AND 4)

Referring to FIG. 3, a data protection system 300 includes a data protection appliance (DPA) cluster 302 a and a storage array 306 a at a production site and a DPA cluster 302 b and a storage array 306 b at a replication site. The DPA clusters 302 a, 302 b are connected by a network 304 (e.g., a WAN, a Fibre Channel and so forth).

The storage array 306 a includes a primary storage volume 312 a, a journal 316 a, a first snapshot 322 a, a second snapshot 322 b, APIs 350 a and a delta marking stream 360. The storage array 306 b includes a replica storage volume 312 b which replicates the primary storage 312 a, a journal 316 b, a list of snapshots 340, and APIs 350 b.

Referring to FIG. 4, an example of a process to send data from the production site to the replication site using a snapshot shipping mode is a process 400. Process 400 generates a first snapshot of a production storage array (402). For example, the DPA cluster 302 a generates a first snapshot 322 a of the primary storage volume 312 a. In one example, the DPA cluster 302 a generates the first snapshot 322 a using the API 350 a. At first time initialization, the first snapshot is sent to the replica site.

Process

400 generates a second snapshot of a production storage array (406). For example, the DPA cluster 302 a generates a second snapshot 322 b of the primary storage volume 312 a. In one example, the DPA cluster 302 a generates the second snapshot 322 b using the API 350 a.

Process

400 obtains differences between the first snapshot and the second snapshot (408). For example, the DPA cluster 302 a obtains the differences between the first snapshot 322 a and the second snapshot 322 b by using the API 350 a.

In one example, obtaining the differences between the first snapshot and the second snapshot may be performed by executing a vendor specific read difference command. The read difference command is a vendor specific command which returns locations of the difference and data in the locations. In one example, the result of executing the read difference command is a sequence of (location, length); (location, length) and so forth. In other examples, the read difference command returns a change bitmap.

Process

400 adds the differences to a delta marking stream (410). For example, the DPA cluster 302 a adds the differences obtained in processing block 408 to the delta marking stream 360 using an the API 350 a.

Process

400 deletes the first snapshot (418). For example, the DPA cluster 302 a deletes the first snapshot 322 a.

Process

400 reads the data that changed in the second snapshot (422) and sends the data to the replication site (440). For example, the DPA cluster 302 a reads the data that changed in the second snapshot 322 b and sends the data to the DPA cluster 302 b.

Process

400 renames the second snapshot to the first snapshot (446) and performs processing block 406. For example, the DPA cluster 302 a renames the second snapshot to the first snapshot.

FIGS. 5 to 7 depict an example of processes used to test the integrity of a replicated storage. FIGS. 5 and 7 depict processes (e.g., a process 500 and a process 700 respectively) that occur at the production site while the FIG. 6 depicts a process (e.g., a process 600) that occurs at replication site.

Theoretically checking the integrity of replication in a snapshot shipping mode is relatively easy. Once a snapshot is shipped to the replica site, both production and replica storage have the same snapshot and the system can just start scrubbing the devices by creating strong hash signature (say SHA-1 or SHA-2) for all the disk or for long parts of the disk (if fine granular errors need to be found). Then once a comparison is complete the system can decide if production and replica volumes are identical or not.

The issue with the above approach is that it requires that the snapshots to be in existence a long time. In particular, the snapshots cannot be erased during the period of checking for integrity. If the replicated volume size is large, the scrubbing can take a significant amount of time and thus keeping the snapshots will require significant amount of memory space.

As will be described herein, the integrity check is started at the beginning of the volume and continues to the end of the volume. The integrity check is performed a portion of the volume at a time. Since the system is in the middle of snapshot shipping, some of the portion may be changed during the shipping of the snapshot. By performing

processes

500, 600 and 700 the snapshots do not need to be kept for long periods of time consuming significant amounts of memory.

Referring to FIG. 5, process 500 generates a snapshot of the production volume to form a snapshot volume (502).

Process

500 goes to a first portion of the snapshot volume (508). The integrity check is performed a portion of the volume at a time. In one particular example, the snapshot volume may be a terabyte and a portion of the snapshot volume may be 10 gigabytes.

Process

500 reads a first area of the portion of the snapshot of the volume (514). In one example, a portion is 10 gigabytes and the first area is 10 megabytes.

Process

500 generates a course granularity hash (518). A course granularity hash signature is a hash signature of the data in a area.

Process

500 generates fine granularity hash signatures (522). The area is further broken down into subareas. A fine granularity hash signature is a hash signature of the data in a subarea. A fine granularity hash signature is generated for each subarea that makes up the area. In one example, a subarea may be a size of a smallest block used for snapshot shipping.

Process

500 determines if the area of memory intersects with a portion of the volume that is under going changes due differences occurring in the production volume from the current snapshot volume (528). While the integrity check is occurring, portions of the production volume may change. Process 500 determines if those differences occurred within the area of memory currently being processed.

If the area of memory does intersect with a portion of the volume that is undergoing changes, process 500 sends the fine granularity hash signatures to the replica site (530).

If the area of memory does not intersect with a portion of the volume that is undergoing changes, process 500 sends the course granularity hash signature to the replica site (536).

Process

500 determines if there are any more areas left to process in the current portion (538). If there are more areas left, process 500 reads the next area (540) and repeats processing block 518.

If there are no more areas left, process 500 determines if there any more portions left in the snapshot volume (542). If there are more portions, process 500 goes to the next portion (546) and reads the first area (514). If there are no more portions, process 500 ends. In some embodiments, if the check of the portion is not complete the system will not move to ship the next snapshots (i.e., going from processing block 446 to processing block 406).

In other embodiments, the integrity check may not delay the snapshot shipping process. In this case when a second snapshot is generated (406), the integrity tool is configured to start reading from the second snapshot, but the differences are added to a special data structure of areas to be ignored.

Referring to FIG. 6, process 600 goes to the first area of the portion of the replica volume (602). Process 600 determines that for the current area whether a course granularity hash signature was received from the production site for the corresponding area in the snapshot volume (608). If a course granularity hash signature was received from the production site, process 600 determines a course granularity hash signature for the corresponding area in the replica volume (614).

Process

600 determines if the course granularity hash signature for a area from the snapshot volume at the production site is the same as the course granularity hash signature for the corresponding area in the replica volume (618). If the course granularity hash signature for an area from the snapshot volume at the production site is not the same as the course granularity hash signature for the corresponding area in the replica volume, process 600 generates and sends fine granularity hash signatures of the subareas of the area in the replica volume to the production site (622).

If a course granularity hash signature was not received from the production site, process 600 determines if fine granularity hash signatures for the corresponding area in the replica volume were received (626). If fine granularity hash signatures were received from the production site, process 600 determines fine granularity hash signatures for the corresponding subareas in the replica volume (632).

Process

600 determines if the fine granularity hash signatures for a area from the snapshot volume at the production site is the same as the fine granularity hash signatures for the corresponding subareas in the replica volume (636). If the fine granularity hash signatures for an area from the snapshot volume at the production site is not the same as the fine granularity hash signatures for the corresponding subareas in the replica volume, process 600 send the locations of those differences to the production site (642).

Process

600 determines if there any more areas left (628) and if there are more areas left, goes to the next area (630) and repeats processing block 608.

If there are not anymore areas left, process 600 determines if there are any portions left (632); and if there are portions left, process 600, goes to the next portion (634) and repeats processing block 602. If there are no portions left, process 600 ends.

Referring to FIG. 7, process 700 determines if fine granularity hash signatures was received from the replica site (702). For example, fine granularity hash signatures sent by the replica site in processing block 622 (FIG. 6).

If there were fine granularity hash signatures received from the replica site, process 700 determines if there are any differences between the fine granularity hash signatures from the replica site and the fine granularity hash signatures at the production site for the corresponding subareas (704). If there are differences, process 700 marks the areas as suspected dirty in a dirty list (710).

Process

700 determines if bad locations were received from the replica site (714). For example, those locations sent by the replica site in processing block 642 (FIG. 6). If there are bad locations received, process 700 marks the locations in the dirty list (716).

Process

700 determines if the system is configured to stop or pause shipping new snapshots of the production volume to the replica site until the integrity testing of a portion is complete (722) and if the system is configured as such, process 700 reports the dirty list as integrity errors (730).

Otherwise, process 700 removes entries from the dirty list that are being changed in the production volume (734). If process 700 determines that the dirty list is not empty (738), process 700 reports the dirty list as a list of integrity errors (742).

Referring to FIGS. 8 and 9, as described above, the portions chosen for processing were not chosen for any particular. However, if portions were chosen where there was a greater chance of finding errors, then finding these errors would occur faster.

Process

800 and 900 are examples of processes to determine which portions of the volume to check first.

Referring to FIG. 8, process 800 checks for regions in a volume with a higher recent activity (810). For example, locations which are more write active in the last few days or since the last cheek are checked first, as these locations are probably more important and if there was corruption due to replication error it is more likely to happen within these blocks. In one particular example, storage tiering statistics of the storage (e.g., EMC® fully automated storage tiering (FAST®)) are used to find the most active areas.

Referring to FIG. 9, process 900 checks regions which are not write active (902). For example, storage statistics are used to determine locations which are not write active. For example, the defect may be caused if the spindles of a device themselves are not functioning well (i.e., some sectors are corrupted). If the sectors are corrupted and active in the system, theses error would be discovered. However, if an area of storage is not accessed or the sectors are only read from then the sectors may not be verified at the replica site since the system does not read from them.

Referring to FIG. 10, in one example, a computer 1000 includes a processor 1002, a volatile memory 1004, a non-volatile memory 1006 (e.g., hard disk) and the user interface (UI) 1008 (e.g., a graphical user interface, a mouse, a keyboard, a display, touch screen and so forth). The non-volatile memory 1006

stores computer instructions

1012, an operating system 1016 and data 1018. In one example, the computer instructions 1012 are executed by the processor 1002 out of volatile memory 1004 to perform all or part of the processes described herein (e.g., processes 500, 600, 700, 800 and 900).

The processes described herein (e.g., processes 500, 600, 700, 800 and 900) are not limited to use with the hardware and software of FIG. 10; they may find applicability in any computing or processing environment and with any type of machine or set of machines that is capable of running a computer program. The processes described herein may be implemented in hardware, software, or a combination of the two. The processes described herein may be implemented in computer programs executed on programmable computers/machines that each includes a processor, a non-transitory machine-readable medium or other article of manufacture that is readable by the processor (including volatile and non-volatile memory and/or storage elements), at least one input device, and one or more output devices. Program code may be applied to data entered using an input device to perform any of the processes described herein and to generate output information.

The system may be implemented, at least in part, via a computer program product, (e.g., in a non-transitory machine-readable storage medium such as, for example, a non-transitory computer-readable medium), for execution by, or to control the operation of, data processing apparatus (e.g., a programmable processor, a computer, or multiple computers)). Each such program may be implemented in a high level procedural or object-oriented programming language to communicate with a computer system. However, the programs may be implemented in assembly or machine language. The language may be a compiled or an interpreted language and it may be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program may be deployed to be executed on one computer or on multiple computers at one site or distributed across multiple sites and interconnected by a communication network. A computer program may be stored on a non-transitory machine-readable medium that is readable by a general or special purpose programmable computer for configuring and operating the computer when the non-transitory machine-readable medium is read by the computer to perform the processes described herein. For example, the processes described herein may also be implemented as a non-transitory machine-readable storage medium, configured with a computer program, where upon execution, instructions in the computer program cause the computer to operate in accordance with the processes. A non-transitory machine-readable medium may include but is not limited to a hard drive, compact disc, flash memory, non-volatile memory, volatile memory, magnetic diskette and so forth but does not include a transitory signal per se.

The processes described herein are not limited to the specific examples described. For example, the

processes

500, 600, 700, 800 and 900 are not limited to the specific processing order of FIGS. 5 to 9, respectively. Rather, any of the processing blocks of FIGS. 5 to 9 may be re-ordered, combined or removed, performed in parallel or in serial, as necessary, to achieve the results set forth above.

In other examples, one of ordinary skill in the art would recognize that increasing and decreasing reference counts may be done opposite as described, For example, the reference count can be decreased and then increased. One of ordinary skill in the art would also recognize that a value is changed from a first state to a second state when the signature data is needed to avoid erasure of the data and when the data is no longer needed the value returns to a first state.

The processing blocks (for example, in the

processes

500, 600, 700, 800 and 900) associated with implementing the system may be performed by one or more programmable processors executing one or more computer programs to perform the functions of the system. All or part of the system may be implemented as, special purpose logic circuitry (e.g., an FPGA (field-programmable gate array) and/or an ASIC (application-specific integrated circuit)). All or part of the system may be implemented using electronic hardware circuitry that include electronic devices such as, for example, at least one of a processor, a memory, a programmable logic device or a logic gate.

Elements of different embodiments described herein may be combined to form other embodiments not specifically set forth above. Other embodiments not specifically described herein are also within the scope of the following claims.

Claims

What is claimed is:

1. A method comprising:

marking a list of locations currently being shipped to a replica site;

generating course granularity hash signatures of data for each area of memory in the snapshot volume, the snapshot volume being a snapshot of a production volume;

generating fine granularity hash signatures of data for each subarea of memory in the snapshot volume;

sending course granularity hash signatures to the replica site for each area not being changed in the production volume; and

sending fine granularity hash signatures to the replica site for each area being changed in the production volume.

2. The method of claim 1, further comprising:

receiving from the replica site fine granularity hash signatures of data for subareas of memory in a replica volume; and

comparing the fine granularity hash signatures from the replica site with the fine granularity hash signatures of the production site for corresponding subareas of memory.

3. The method of claim 2, further comprising:

comparing the fine granularity hash signatures received from the production site with the fine granularity hash signatures of the replica volume for corresponding subareas of memory; and

sending from the replica site the potential locations of corruption in the replica volume for the fine granularity hash signatures received from the production site that do not match with the fine granularity hash signatures of the replica volume.

4. The method of claim 3, further comprising:

comparing the course granularity hash signatures received from the production site with the course granularity hash signatures of the replica volume for corresponding areas of memory; and

sending, from the replica site to the production site, fine granularity hash signatures for those subareas within area of memory where the course granularity hash signature received form the production site does not match the course granularity hash signature of the corresponding area in the replica volume.

5. The method of claim 1, wherein a sub-area is equal to a smallest block used in snapshot shipping.

6. The method of claim 1, further comprising checking first at least one of areas within the replica volume with a higher recent activity during an integrity test or areas within the replica volume which are not write active during an integrity test.

7. The method of claim 1, further comprising, if a new snapshot of the production volume is configured to be shipped to the replica site, adding differences between fine granularity hash signatures from the replica site and the fine granularity hash signatures at the production site to a suspected difference list.

8. The method of claim 7, further comprising:

removing entries from the suspected difference list for locations being updated in the production volume; and

reporting the suspected list as errors if the suspected list is not empty.

9. The method of claim 1, further comprising pausing shipping a snapshot of the production volume from the production site to the replica site if an integrity check of a portion of a volume is not complete.

10. The method of claim 9, further comprising reporting as errors differences between fine granularity hash signatures from the replica site and the fine granularity hash signatures at the production site.

11. An apparatus, comprising:

electronic hardware circuitry configured to:

mark a list of locations currently being shipped to a replica site;

generate course granularity hash signatures of data for each area of memory in the snapshot volume, the snapshot volume being a snapshot of a production volume;

generate fine granularity hash signatures of data for each subarea of memory in the snapshot volume;

send course granularity hash signatures to the replica site for each area not being changed in the production volume; and

send fine granularity hash signatures to the replica site for each area being changed in the production volume;

wherein the circuitry comprises at least one of a processor, a memory, a programmable logic device or a logic gate.

12. The apparatus of claim 11, further comprising circuitry configured to:

receive from the replica site fine granularity hash signatures of data for subareas of memory in a replica volume;

compare the fine granularity hash signatures from the replica site with the fine granularity hash signatures of the production site for corresponding subareas of memory;

compare the fine granularity hash signatures received from the production site with the fine granularity hash signatures of the replica volume for corresponding subareas of memory;

send from the replica site the potential locations of corruption in the replica volume for the fine granularity hash signatures received from the production site that do not match with the fine granularity hash signatures of the replica volume;

compare the course granularity hash signatures received from the production site with the course granularity hash signatures of the replica volume for corresponding areas of memory; and

send, from the replica site to the production site, fine granularity hash signatures for those subareas within area of memory where the course granularity hash signature received form the production site does not match the course granularity hash signature of the corresponding area in the replica volume.

13. The apparatus of claim 11, further comprising circuitry configured to check first at least one of areas within the replica volume with a higher recent activity during an integrity test or areas within the replica volume which are not write active during an integrity test.

14. The apparatus of claim 11, further comprising circuitry configured to if a new snapshot of the production volume is configured to be shipped to the replica site:

add differences between fine granularity hash signatures from the replica site and the fine granularity hash signatures at the production site to a suspected difference list;

remove entries from the suspected difference list for locations being updated in the production volume; and

report the suspected list as errors if the suspected list is not empty.

15. The apparatus of claim 11, further comprising circuitry configured to:

pause shipping a snapshot of the production volume from the production site to the replica site if an integrity check of a portion of a volume is not complete; and

report as errors differences between fine granularity hash signatures from the replica site and the fine granularity hash signatures at the production site.

16. An article comprising:

a non-transitory computer-readable medium that stores computer-executable instructions, the instructions causing a machine to:

mark a list of locations currently being shipped to a replica site;

send fine granularity hash signatures to the replica site for each area being changed in the production volume.

17. The article of claim 16, further comprising instructions causing the machine to:

send from the replica site the potential locations of corruption in the replica volume for the fine granularity hash signatures received from the production site that do not match with the fine granularity hash signatures of the replica volume.

18. The article of claim 16, further comprising instructions causing the machine to check first at least one of areas within the replica volume with a higher recent activity during an integrity test or areas within the replica volume which are not write active during an integrity test.

19. The article of claim 16, further comprising instructions causing the machine to if a new snapshot of the production volume is configured to be shipped to the replica site:

report the suspected list as errors if the suspected list is not empty.

20. The article of claim 16, further comprising instructions causing the machine to: